While current and former commission members described the ruling as "nuanced," "thorough" and "pretty precise," the ultimate impact on the commission's two-plus-year review was not immediately clear.

Commission Chairman Dr. Nazim Peerwani, Tarrant County's chief medical examiner, said he arranged for copies of the ruling, which he termed "a good guide going forward," to be sent to the panel's seven members.

"We will debate what impact the opinion has on Willingham at our meeting in September," he said. "It's something we will collectively decide."

The commission, which in April issued stern recommendations for improved fire investigation training, had requested Abbott's opinion. The panel had delayed deciding whether Corsicana and state arson investigators were guilty of negligence or professional misconduct in the case pending the attorney general's ruling.

The case centers around a 1991 Christmas-season house fire in which Willingham's three young children died. Willingham, 36, consistently protested his innocence. He was executed in February 2004.

Three professional reviews of the arson investigations — including one authorized by the forensics commission - found fault with the probes. Shortly after the Corsicana investigations, the National Fire Protection Association issued arson-investigation standards that rendered many earlier procedures obsolete.

The three professional reviews focused on the arson investigations and drew no conclusions on Willingham's guilt or innocence. Likewise, the Forensic Sciences Commission's review focused solely on the quality of the investigations.

Until the commission hired its own legal adviser in December, a member of Abbott's staff attended the panel's meetings and offered it legal advice.

Abbott on Friday ruled the commission lacked authority to launch investigations of forensic laboratories that were not accredited at the time of the incident. At the time of the Corsicana fire, the state had no mechanism for lab accreditation.

Restriction on evidence

The attorney general also held that while the commission can investigate cases pre-dating its Sept. 1, 2005, creation, it cannot review evidence that was tested or introduced into evidence before that time.

Williamson County District Attorney John Bradley, who headed the commission until recently, said Abbott's ruling mirrored his own assessment of the case.

"I'm not on the commission, so I don't know what it will do," he said, adding that, given Abbott's ruling, moving forward with the investigation "would really threaten the rule of law."

Through his press secretary, Katherine Cesinger, Gov. Rick Perry said Abbott's ruling will clear the way for the commission to "focus on fulfilling the important role that the Legislature has assigned to it."

Steve Saloom, policy director of the New York-based Innocence Project, whose formal complaint launched the investigation, said the ruling should not affect the commission's investigation.

"The Willingham allegation has always been about the fire marshal's continued failure - it continues to this day - to inform the criminal justice system that the analyses often used in Texas to determine arson were long ago proved invalid," he said.

State Sen. Rodney Ellis, D-Houston, concurred, saying "nothing in this attorney general's opinion prevents the Texas Forensic Science Commission from completing its report and ruling that the fire marshal was negligent when it failed in its duty to correct the flawed arson science that was used in numerous arson cases."

Questions about the Willingham arson investigations arose days before his execution, when Austin fire expert Gerald Hurst reviewed them at the request of the accused man's cousin.

'Mystics or psychics'

Hurst found the arson sleuths' work flawed, but his report was not sufficient to save Willingham's life. Later, a five-expert panel assembled by the Innocence Project and commission-hired Baltimore fire expert Craig Beyler also ripped the earlier investigations.

Beyler said the state's detective work was "characteristic of mystics or psychics."

In a later appearance before the panel, Ed Salazar, a lawyer who is second-in-command at the Texas Fire Marshal's Office, defended his investigator's work, saying it was sound then and is now. The commission, he charged in a thinly veiled thrust at the Innocence Project, had fallen under the influence of an outside group with an "agenda."

In late September 2009, two days before Beyler was to address the panel, Perry removed then-chairman Sam Bassett, an Austin lawyer, and two other members, saying their terms had expired.

With Bradley in the chairman's seat, commission sessions frequently degenerated into verbal wrangles. Last summer, commissioners rejected a Bradley-favored final report that stopped short of finding negligence.

At another point, they criticized the chairman for asserting Willingham had been a "guilty monster."

Texas lawmakers in May refused to ratify Perry's nomination of Bradley for a second term as chairman.